The nonmetallocene catalyst, also called as the post-metallocene catalyst, was discovered in middle and late 1990's, whose central atom involves nearly all of the transition metal elements. The nonmetallocene catalyst is comparative to, or exceeds, the metallocene catalyst in some aspects of the performance, and has been classified as the fourth generation catalyst for olefin polymerization, following the Ziegler catalyst, the Ziegler-Natta catalyst and the metallocene catalyst. Polyolefin products produced with such catalysts exhibit favorable properties and boast low production cost. The coordination atom of the nonmetallocene catalyst comprises oxygen, nitrogen, sulfur and phosphor, without containing a cyclopentadiene group or a derivative thereof (for example, an indene group or a fluorene group). The nonmetallocene catalyst is wherein its central atom shows comparatively strong electrophilicity and has a cis alkyl metal type or a metal halide type central structure, which facilitates olefin insertion and σ-bond transfer. Therefore, the central atom is easily subject to alkylation, and therefore facilitates formation of a cationic active center. The thus formed complex has a restricted geometrical configuration, and is stereoselective, electronegative and chiral adjustable. Further, the formed metal-carbon bond is easy to be polarized, which further facilitates homopolymerization and copolymerization of an olefin. For these reasons, it is possible to obtain an olefin polymer having a comparatively high molecular weight, even under a comparatively high polymerization temperature.
However, it is known that in the olefin polymerization, the homogeneous phase catalyst suffers from such problems as short service life, fouling, high consumption of methyl aluminoxane, and undesirably low or high molecular weight in the polymer product, and thus only finds limited use in the solution polymerization process or the high-pressure polymerization process, which hinders its wider application in industry.
Chinese patent Nos. ZL01126323.7, ZL02151294.9 and ZL02110844.7, and WO03/010207 disclose a catalyst or catalyst system finding a broad application in olefin polymerization, and suitable for many forms of polymerization process. However, the catalyst or catalyst system should be accompanied by a comparatively high amount of co-catalysts, to achieve an acceptable olefin polymerization activity. Further, the catalyst or catalyst system suffers from such a problem as fouling.
A conventional way is to have the nonmetallocene catalyst supported. By supporting, It is possible to avoid deactivation of the dual molecular in the homogeneous phase nonmetallocene catalyst, whereby improving the performance of the catalyst in the polymerization and the particle morphology of the polymer products. This is reflected by, moderate reduction of the initial activity of the catalyst, elongation of the serve life of the catalyst, alleviation or elimination of caking or flash reaction during the polymerization, improvement of the polymer morphology, and increase of the apparent density of the polymer, thus extending its use to other polymerization processes, for example, the gas phase polymerization or the slurry polymerization.
Aiming at the catalysts of the Chinese patent Nos. ZL01126323.7, ZL02151294.9 and ZL02110844.7, and WO03/010207, Chinese patent application Laid-Open Nos. CN1539855A, CN1539856A, CN1789291A, CN1789292A and CN1789290A, and WO2006/063501 and Chinese patent application No. 200510119401.x provide several ways to support same on a carrier so as to obtain a supported nonmetallocene catalyst. However, each of these applications relates to the technology of supporting a transition metal-containing nonmetallocene organic compound (or referred as a nonmetallocene catalyst, or a nonmetallocene complex) on a treated carrier. However, the bonding between the nonmetallocene catalyst and the carrier is rather limited, or the load of the nonmetallocene catalyst on the carrier is rather low.
Most of the prior art olefin polymerization catalysts are metallocene catalyst-based, for example, those according to U.S. Pat. No. 4,808,561 and U.S. Pat. No. 5,240,894, Chinese patent application Laid-Open Nos. CN1049439, CN1136239, CN1344749, CN1126480, CN1053673, CN1307594, CN1130932, CN1103069, CN1363537 and CN1060179, U.S. Pat. No. 574,417, EP 685494, U.S. Pat. No. 4,871,705 and EP0206794. Again, all of these applications relate to the technology of supporting a transition metal-containing metallocene catalyst on a treated carrier.
EP708116 discloses a process comprising treating gasified ZrCl4 with a carrier at a temperature ranging from 160° C. to 450° C. to support thereon, then reacting the supported ZrCl4 with the Li-salt of a ligand to obtain a supported metallocene catalyst, which is finally used for olefin polymerization in combination with a co-catalyst. The process is rather undesirable since the supporting procedure should be conducted at a high reaction temperature and under a high vacuum.
Chinese application patent No. ZL01131136.3 discloses a process for producing a supported metallocene catalyst, which comprises mixing a carrier with a Group IVB transition metal halide in a solvent under the normal pressure, then directly reacting with the cation ion of a ligand, so as to integrate synthesis and supporting of the metallocene catalyst in one step. However, according to this process, the transition metal and the ligand is used at a molar ratio of 1:1, and a proton acceptor (for example, butyl lithium) is required. Further, the ligand to be used is a bridged or non-bridged metallocene ligand containing a cyclopentadiene group.
According to Xiao's article “Study on a novel Ni(acac)2/TiCl4/L ligand composite catalyst in ethylene polymerization to produce branched polyethylene” (Zhongshan Daxue Xuebao: Natural Science Edition, 2003, 42(3):28), anhydrous MgCl2, Ni(acac)2 and L are dissolved in a mixed solvent of tetrahydrofuran and ethanol, then silica gel is added thereto under stirring. Further, a determined amount of TiCl4 is added thereto to react for a predetermined duration. Then, a predetermined amount of Et2AlCl is added thereto to react for another predetermined duration. Finally, the resultant is dried by suction to obtain a composite catalyst comprising MgCl2-silica as the carrier and an α-diimine ligand L-modified Ni(acac)2/TiCl4 supported thereon. By using said catalyst in ethylene homopolymerization, branched polyethylene can be obtained. Specifically, in case of the ligand L2, branched polyethylene having a branch degree of 4 to 12 branched chains/1000 C can be obtained.
By using a supported nonmetallocene catalyst comprising silica gel as the carrier or as a component of the carrier, a polymer product having desirable particle morphology and controlled polymer particle size distribution can be obtained. However, the thus obtained catalyst suffers from comparatively low polymerization activity. Further, since the ash contains silica gel, the polymer thus obtained finds only restricted application.
According to EUROPEAN POLYMER JOURNAL, 2005, 41, 941 to 947, a supported metallocene catalyst can be obtained by treating MgCl2(THF)2 with chloro ethyl aluminum, and supporting zirconocene dichloride thereon. Specifically, MgCl2 is dissolved in tetrahydrofuran, after precipitated by hexane and washed, the thus obtained solid is treated by chloro ethyl aluminum, and then supported with zirconocene dichloride.
According to Sun's article “Study of an in-situ process for preparing CpTi(dbm)Cl2/MgCl2 type catalyst and its use for catalyzing ethylene polymerization” (Gaofenzi Xuebao, 2004, (1):138), magnesium chloride (as the carrier) is prepared by the Grignard reagent process, and at the same time, CpTi(dbm)Cl2 is added thereto, so as to produce said CpTi(dbm)Cl2/MgCl2 type catalyst. According to said article, alkylation and supporting of the catalyst is conducted in one single step, and therefore the number of the steps for preparing the catalyst can be significantly reduced.
Chinese patent No. ZL200510080210.7 discloses a process for in-situ producing a supported vanadium-based nonmetallocene catalyst for olefin polymerization and use thereof, which comprises reacting dialkyl magnesium with acyl naphthol or a β-dione to form magnesium acyl naphthol or magnesium β-dione compound, then reacting with a chloride of vanadium (IV), so as to form the carrier and the active catalytic component simultaneously.
Chinese patent No. ZL200610026765.8 discloses a single site Zeigler-Natta catalyst for olefin polymerization. In this catalyst, a coordination group-containing salicylaldehyde or substituted salicylaldehyde derivative is used as the electron donor. The catalyst is produced by introducing a pre-treated carrier (for example, silica), a metallic compound (for example, TiCl4) and the electron donor into a magnesium compound (for example, MgCl2)/tetrahydrofuran solution and then post-treating the resultant.
Chinese patent No. ZL200610026766.2 is similar to this patent, and relates to an organic compound containing a hetero atom and use thereof for producing a Zeigler-Natta catalyst.
As can be seen from aforesaid, the prior art supported nonmetallocene catalyst suffers from low olefin polymerization activity, and there is no an easy way to adjust same. If one tries to increase the activity, he has to significantly increase the amount of the co-catalyst to be used. Further, the prior art catalyst contains such carrier as silica gel for supporting, and therefore the polymer obtained therewith contains brittle ash remains resulted from the silica gel. For this reason, the polymer finds only limited application in practice. Still further, the polymer product (for example, polyethylene) produced by using the prior art catalyst suffers from low polymer bulk density.
Therefore, there still exists a need for a supported nonmetallocene catalyst, which can be produced in a simple way and in an industrial scale, free of the problems associated with the prior art catalyst.